The present invention relates to a soldering apparatus and method for automatically soldering chips and other electronic parts to a printed circuit board.
Typically, a conventional soldering apparatus includes a conveyor for conveying a printed circuit board and a flux applicator located below the conveyor and adapted to apply flux to the printed circuit board. A preheater is located below the conveyor and upstream of the flux applicator and adapted to preheat the printed circuit board. A wave soldering bath is located below the conveyor and downstream of the preheater and adapted to solder chips and other electronic parts to the printed circuit board. A cooling unit is located below the conveyor and downstream of the wave soldering bath and adapted to cool the printed circuit board.
The flux typically contains natural or wood rosin and an activator and is dissolved in alcohol such as isopropyl alcohol. The flux in alcohol is applied to the printed circuit board by the flux applicator. There are currently available two types of flux applicators, that is, a foamed flux applicator and a flux spray. The foamed flux applicator includes a container within which flux dissolved in alcohol is contained, and a porous tube located below the container and adapted to utilize air under pressure to provide foamed flux. A printed circuit board is then brought into contact with the foamed flux. The flux spray includes a supply of flux in alcohol, and a spray nozzle for spraying a mist of the flux onto a printed circuit board. Either of the flux applicators employs flux in alcohol. Typically, the flux contains from 10 to 20 percent by weight of natural rosin together with an activator and 80 to 90 percent by weight of alcohol.
A disadvantage with the use of the flux in alcohol is that fire may occur if great care is not taken. Specifically, the flux in alcohol is subject to volatilization as it is often contacted with the pressurized air. If natural rosin is left within the apparatus, dust may be firmly attached to the rosin. Fire may occur when the volatilized alcohol is absorbed in the dust and exposed to heat dissipated from a preheater or a soldering bath.
Recently, the use of flux in alcohol or volatile organic compound (VOC) is limited, for example, by the laws of the State of California, U.S.A. The volatile organic compound, when exposed to ultraviolet light, produces harmful ozone as a result of photochemical reaction.
There is, thus, a need to provide a soldering flux without the use of any alcohol. Attempts have been made to suspend natural rosin in water. However, such a flux gives off an unpleasant odor during soldering since it uses amine for suspension of the natural rosin. Also, flux residue is corrosive and must therefore be removed to provide as clean a substrate as possible. This type of flux is thus impractical.
Accordingly, it is an object of the present invention to provide a soldering apparatus and method, which has nothing to do with the volatile organic compound regulations, which do not give off any unpleasant odor, and which eliminates the need to clean a substrate.